Additive manufacturing systems and method of filling voids in 3d parts

ABSTRACT

A method of additive three-dimensional object production includes depositing liquefied material to produce two roads and placing an extruder tip having a bottom surface that surrounds an orifice such that one portion of the bottom surface is sealed against one of the two roads and another part of the bottom surface is sealed against the other of the two roads and the orifice is positioned over a space between the two roads. Liquefied material is then extruded through the orifice to fill the space between the two roads.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on and claims the benefit of U.S.provisional patent application Ser. No. 62/266,313, filed Dec. 11, 2015,the content of which is hereby incorporated by reference in itsentirety.

BACKGROUND

The present disclosure relates to additive manufacturing systems forprinting or otherwise producing three-dimensional (3D) parts and supportstructures. In particular, the present disclosure relates to toolpathsfor printing 3D parts and support structures in a layer-by-layer mannerusing an additive manufacturing technique.

Additive manufacturing systems are used to print or otherwise build 3Dparts from digital representations of the 3D parts (e.g., AMF and STLformat files) using one or more additive manufacturing techniques.Examples of commercially available additive manufacturing techniquesinclude extrusion-based techniques, jetting, selective laser sintering,high speed sintering, powder/binder jetting, electron-beam melting, andstereolithographic processes. For each of these techniques, the digitalrepresentation of the 3D part is initially sliced into multiplehorizontal layers. For each sliced layer, a tool path is then generated,which provides instructions for the particular additive manufacturingsystem to print the given layer.

For example, in an extrusion-based additive manufacturing system, a 3Dpart may be printed from a digital representation of the 3D part in alayer-by-layer manner by extruding a flowable part material. The partmaterial is extruded through an extrusion tip carried by a print head ofthe system, and is deposited as a sequence of roads on a platen inplanar layers. The extruded part material fuses to previously depositedpart material, and solidifies upon a drop in temperature. The positionof the print head relative to the substrate is then incremented, and theprocess is repeated to form a 3D part resembling the digitalrepresentation.

In fabricating 3D parts by depositing layers of a part material,supporting layers or structures are typically built underneathoverhanging portions or in cavities of 3D parts under construction,which are not supported by the part material itself. A support structuremay be built utilizing the same deposition techniques by which the partmaterial is deposited. The host computer generates additional geometryacting as a support structure for the overhanging or free-space segmentsof the 3D part being formed. Support material is then deposited pursuantto the generated geometry during the printing process. The supportmaterial adheres to the part material during fabrication, and isremovable from the completed 3D part when the printing process iscomplete.

SUMMARY

An aspect of the present disclosure is directed to a method of additivethree-dimensional object production includes depositing liquefiedmaterial to produce two roads and placing an extruder tip having abottom surface that surrounds an orifice such that one portion of thebottom surface is sealed against one of the two roads and another partof the bottom surface is sealed against the other of the two roads andthe orifice is positioned over a space between the two roads. Liquefiedmaterial is then extruded through the orifice to fill the space betweenthe two roads.

Another aspect of the present disclosure is directed to an additivemanufacturing system that includes a nozzle having an orifice surroundby a bottom surface. A controller in the system receives instructions toprint along two tool paths and to print along a void filling pathbetween the two tool paths. The controller sends control signals toprint two roads corresponding to the two tool paths. The controller thensends control signals to move the nozzle along the void filling pathbetween the two roads such that the two roads remain in contact with thebottom surface of the nozzle while the controller also sends controlsignals to extrude material to fill a void between the two roads.

In a still further aspect, a method comprises extruding material from anextruder tip of an additive manufacturing system such that the extrudedmaterial flows beneath and between portions of two previously extrudedroads of material.

DEFINITIONS

Unless otherwise specified, the following terms as used herein have themeanings provided below:

The terms “preferred”, “preferably”, “example” and “exemplary” refer toembodiments of the invention that may afford certain benefits, undercertain circumstances. However, other embodiments may also be preferredor exemplary, under the same or other circumstances. Furthermore, therecitation of one or more preferred or exemplary embodiments does notimply that other embodiments are not useful, and is not intended toexclude other embodiments from the scope of the present disclosure.

Directional orientations such as “above”, “below”, “top”, “bottom”, andthe like are made with reference to a layer-printing direction of a 3Dpart. In the embodiments shown below, the layer-printing direction isthe upward direction along the vertical z-axis. In these embodiments,the terms “above”, “below”, “top”, “bottom”, and the like are based onthe vertical z-axis. However, in embodiments in which the layers of 3Dparts are printed along a different axis, such as along a horizontalx-axis or y-axis, the terms “above”, “below”, “top”, “bottom”, and thelike are relative to the given axis.

The term “providing”, such as for “providing a material”, when recitedin the claims, is not intended to require any particular delivery orreceipt of the provided item. Rather, the term “providing” is merelyused to recite items that will be referred to in subsequent elements ofthe claim(s), for purposes of clarity and ease of readability.

Unless otherwise specified, temperatures referred to herein are based onatmospheric pressure (i.e. one atmosphere).

The terms “about” and “substantially” are used herein with respect tomeasurable values and ranges due to expected variations known to thoseskilled in the art (e.g., limitations and variabilities inmeasurements).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an additive manufacturing system configured toprint 3D parts and support structures with the use of one or more printhead liquefier assemblies of the present disclosure.

FIG. 2 is a plan view of an exemplary print head 18.

FIG. 3 is a sectional view of a casing assembly of an exemplary printhead in accordance with one embodiment.

FIG. 4 is a sectional view of a casing assembly of a print head inaccordance with a second embodiment.

FIG. 5 is a top view of two neighboring printed roads under the priorart.

FIG. 6 is a sectional view of the two printed roads of FIG. 5.

FIG. 7 is a top view of two spaced roads printed in accordance with someembodiments.

FIG. 8 is a sectional view of the spaced roads of FIG. 7.

FIG. 9 is a top view showing a nozzle filling the voids between the tworoads of FIG. 7.

FIG. 10 is a sectional view of FIG. 9.

FIG. 11 is an enlarged sectional view of two spaced apart roads with afirst spacing.

FIG. 12 is a sectional view of two spaced apart roads with a secondspacing.

FIG. 13 is a top view showing a fill pattern of the prior art.

FIG. 14 is a sectional view of FIG. 13.

FIG. 15 is a top view of spaced apart roads in accordance with oneembodiment.

FIG. 16 is a sectional view of FIG. 15.

FIG. 17 is the sectional view of FIG. 16 while the voids in FIG. 16 arebeing filled.

FIG. 18 is a perspective view of a fill pattern under the prior art.

FIG. 19 is a perspective view of spaced roads for a fill pattern inaccordance with one embodiment.

FIG. 20 is a perspective view of the fill pattern of FIG. 19 during thefilling of voids of the spaced roads.

FIG. 21 is a perspective view of a prior art fill pattern at a boundaryroad.

FIG. 22 provides a perspective view of a fill pattern at a boundary roadin accordance with one embodiment during the filling of voids betweenspaced roads.

FIG. 23 is a top view of a fill pattern at a boundary in accordance withone embodiment during the filling of the voids between the boundary andthe fill pattern.

FIG. 24 is a sectional view of a nozzle in accordance with oneembodiment.

FIG. 25 provides a sectional view of a nozzle in accordance with asecond embodiment.

FIG. 26 provides a sectional view of a nozzle in accordance with a thirdembodiment.

FIG. 27 provides a top sectional view of a portion of a print head inaccordance with one embodiment.

FIG. 28 provides a sectional view of a nozzle tip in accordance withsome embodiments.

DETAILED DESCRIPTION

One of the main issues with extrusion-based additive manufacturing ispart strength. In particular, parts made with extrusion-based additivemanufacturing tend to be more brittle than injection molded parts andtend to have much higher anisotropic part strength (stronger in onedirection than another). For example, for one extrusion-based additivemanufacturing technique, parts made from ULTEM™ 9085 resin elongate 2.2%before breaking in the Z direction while injection-molded parts made ofULTEM™ 9085 resin elongate 72% before breaking in the Z direction. Thus,the injection-molded parts are 32 times less brittle than the additivemanufacturing parts. Further, a part made from ULTEM™ 9085 resin usingthe extrusion-based additive manufacturing technique has high isotropicpart strength with a Tensile Strength, Ultimate in the Z direction of 42MPa and a Tensile Strength, Ultimate in the XY directions of 69 MPa.This means that the part is only 61% as strong in the Z direction as inthe XY directions. Injection molded parts made from ULTEM™ 9085 resin donot have isotropic strengths of this magnitude.

One of the key causes of poor part strength and the higher isotropicpart strength is porosity in the additive-manufacturing parts.Embodiments describe below fill parts to a much higher percentage whichreduces the isotropic nature of the part strength and increases Z partstrength.

Embodiments described herein generate tool paths for printingspaced-apart roads such that neighboring roads are not in contact witheach other. The spacing is set such that portions of a bottom surface ofa print nozzle can seal against a top surface of two neighboring spacedapart roads while the nozzle extrudes material to fill the voids betweenthe two roads. As a result of the sealing between the bottom surface ofthe nozzle and the previously printed roads, the extrudate is forcedinto the voids formed underneath portions of each of the previouslyprinted roads. In some embodiments, the amount of material extruded tofill the voids is calculated based on the shapes of the previouslyprinted roads and the spacing between the previously printed roads. Inother embodiments, pressure feedback is used to adjust the amount ofmaterial extruded through the nozzle. Examples of such pressure feedbackinclude a strain gauge on the nozzle, a pressure gauge fluidicallycoupled to the molten material in the nozzle and an accumulator thatreceives molten material when the pressure of the molten materialexceeds a threshold pressure and that releases molten material when thepressure once again drops below the threshold. In still furtherembodiments, radar sensors are used to sense the volume of the voidsbetween two previously printed roads and this volume is used to adjustthe amount of material deposited in the void.

Embodiments of the present disclosure may be used with any suitableextrusion-based additive manufacturing system. FIG. 1 shows one suchsystem 10 that is an additive manufacturing system for printing 3D partsor models and corresponding support structures (e.g., 3D part 22 andsupport structure 24) from part and support material filaments,respectively, of consumable assemblies 12, using a layer-based, additivemanufacturing technique. Suitable additive manufacturing systems forsystem 10 include extrusion-based systems developed by Stratasys, Inc.,Eden Prairie, Minn., such as fused deposition modeling systems under thetrademark “FDM”.

In FIG. 1, there are two consumable assemblies 12, where one of theconsumable assemblies 12 contains a part material filament, and theother consumable assembly 12 contains a support material filament.However, both consumable assemblies 12 may contain part materialfilaments in some embodiments. Each consumable assembly 12 is an easilyloadable, removable, and replaceable container device that retains asupply of a consumable filament for printing.

In the shown embodiment, each consumable assembly 12 includes containerportion 14, guide tube 16, and print heads 18, where each print head 18preferably includes an extruder 20 of the present disclosure. Containerportion 14 may retain a spool, coil, or other supply arrangement of aconsumable filament, such as discussed in Mannella et al., U.S.Publication Nos. 2013/0161432 and 2013/0161442; and in Batchelder etal., U.S. Publication No. 2014/0158802.

Guide tube 16 interconnects container portion 14 and print head 18,where a drive mechanism of print head 18 (and/or of system 10) drawssuccessive segments of the consumable filament from container portion14, through guide tube 16, to the extruder 20 of the print head 18. Inthis embodiment, guide tube 16 and print head 18 are subcomponents ofconsumable assembly 12, and may be interchanged to and from system 10with each consumable assembly 12. Alternatively, as discussed below,guide tube 16 and/or print head 18 (or parts thereof) may be componentsof system 10, rather than subcomponents of consumable assemblies 12.

As shown, system 10 includes system housing 26, chamber 28, platen 30,platen gantry 32, head carriage 34, and head gantry 36. System housing26 is a structural component of system 10 and may include multiplestructural sub-components such as support frames, housing walls, and thelike. In some embodiments, system housing 26 may include container baysconfigured to receive container portions 14 of consumable assemblies 12.In alternative embodiments, the container bays may be omitted to reducethe overall footprint of system 10. In these embodiments, containerportions 14 may stand adjacent to system housing 26, while providingsufficient ranges of movement for guide tubes 16 and print heads 18.

Chamber 28 is an enclosed environment that contains platen 30 forprinting 3D part 22 and support structure 24. Chamber 28 may be heated(e.g., with circulating heated air) to reduce the rate at which the partand support materials solidify after being extruded and deposited (e.g.,to reduce distortions and curling). In alternative embodiments, chamber28 may be omitted and/or replaced with different types of buildenvironments. For example, 3D part 22 and support structure 24 may bebuilt in a build environment that is open to ambient conditions or maybe enclosed with alternative structures (e.g., flexible curtains).

Platen 30 is a platform on which 3D part 22 and support structure 24 areprinted in a layer-by-layer manner, and is supported by platen gantry32. In some embodiments, platen 30 may engage and support a buildsubstrate, which may be a tray substrate as disclosed in Dunn et al.,U.S. Pat. No. 7,127,309, fabricated from plastic, corrugated cardboard,or other suitable material, and may also include a flexible polymericfilm or liner, painter's tape, polyimide tape (e.g., under the trademarkKAPTON from E.I. du Pont de Nemours and Company, Wilmington, Del.), orother disposable fabrication for adhering deposited material onto theplaten 30 or onto the build substrate. Platen gantry 32 is a gantryassembly configured to move platen 30 along (or substantially along) thevertical z-axis.

Head carriage 34 is a unit configured to receive one or more removableprint heads, such as print heads 18, and is supported by head gantry 36.Examples of suitable devices for head carriage 34, and techniques forretaining print heads 18 in head carriage 34, include those disclosed inSwanson et al., U.S. Pat. Nos. 8,403,658 and 8,647,102. In somepreferred embodiments, each print head 18 is configured to engage withhead carriage 34 to securely retain the print head 18 in a manner thatprevents or restricts movement of the print head 18 relative to headcarriage 34 in the x-y build plane, but allows the print head 18 to becontrollably moved out of the x-y build plane (e.g., servoed, toggled,or otherwise switched in a linear or pivoting manner).

Head gantry 36 is a belt-driven gantry assembly configured to move headcarriage 34 (and the retained print heads 18) in (or substantially in) ahorizontal x-y plane above chamber 28. Examples of suitable gantryassemblies for head gantry 36 include those disclosed in Comb et al.,U.S. Publication No. 2013/0078073, where head gantry 36 may also supportdeformable baffles (not shown) that define a ceiling for chamber 28. Inalternative embodiments, head gantry 36 may utilize any suitablemechanism for moving head carriage 34 (and the retained print heads 18),such as robotic actuators, and the like.

In a further alternative embodiment, platen 30 may be configured to movein the horizontal x-y plane within chamber 28, and head carriage 34 (andprint heads 18) may be configured to move along the z-axis. Othersimilar arrangements may also be used such that one or both of platen 30and print heads 18 are moveable relative to each other. Platen 30 andhead carriage 34 (and print heads 18) may also be oriented alongdifferent axes. For example, platen 30 may be oriented vertically andprint heads 18 may print 3D part 22 and support structure 24 along thex-axis or the y-axis. In another example, platen 30 and/or head carriage34 (and print heads 18) may be moved relative to each other in anon-Cartesian coordinate system, such as in a polar coordinate system.

Additional examples of suitable devices for print heads 18, and theconnections between print heads 18, head carriage 34, and head gantry 36include those disclosed in Crump et al., U.S. Pat. No. 5,503,785;Swanson et al., U.S. Pat. No. 6,004,124; LaBossiere, et al., U.S. Pat.Nos. 7,384,255 and 7,604,470; Batchelder et al., U.S. Pat. Nos.7,896,209 and 7,897,074; and Comb et al., U.S. Pat. No. 8,153,182. Forinstance, extruder 20 may optionally be retrofitted into an existingadditive manufacturing system.

System 10 also includes controller assembly 38, which is one or morecomputer-based systems configured to operate the components of system10. Controller assembly 38 may communicate over communication line(s) 40with the various components of system 10, such as print heads 18(including extruder 20), chamber 28 (e.g., with a heating unit forchamber 28), head carriage 34, motors for platen gantry 32 and headgantry 36, and various sensors, calibration devices, display devices,and/or user input devices.

Additionally, controller assembly 38 may also communicate overcommunication line 42 with external devices, such as other computers andservers over a network connection (e.g., a local area network (LAN)connection, a universal serial bus (USB) connection, or the like). Whilecommunication lines 40 and 42 are each illustrated as a single signalline, they may each include one or more electrical, optical, and/orwireless signal lines and intermediate control circuits, where portionsof communication line(s) 40 may also be subcomponents of the removableprint heads 18.

In some embodiments, the one or more computer-based systems ofcontroller assembly 38 are internal to system 10, allowing a user tooperate system 10 over a network communication line 42, such as from anexternal computer in the same or similar manner as a two-dimensionalprinter. Alternatively, controller assembly 38 may also include one ormore external computer-based systems (e.g., desktop, laptop,server-based, cloud-based, tablet, mobile media device, and the like)that may communicate with the internal computer-based system(s) ofcontroller assembly 38, as well as communicating over a network viacommunication line 42.

In this alternative embodiment, the processing functions of controllerassembly 38 discussed below may be divided between the internal andexternal computer-based systems. In yet another alternative embodiment,the computer-based system(s) of controller assembly 38 may all belocated external to system 10 (e.g., one or more external computers),and may communicate with system 10 over communication line(s) 40.

During a printing operation, controller assembly 38 may direct platengantry 32 to move platen 30 to a predetermined height within chamber 28.Controller assembly 38 may then direct head gantry 36 to move headcarriage 34 (and the retained print heads 18) around in the horizontalx-y plane above chamber 28. Controller assembly 38 may also commandprint heads 18 to selectively draw successive segments of the consumablefilaments from container portions 14 and through guide tubes 16,respectively.

The successive segments of each consumable filament are then melted inthe extruder 20 of the respective print head 18 to produce a moltenmaterial, as discussed below. Upon exiting extruder 20, the resultingextrudate may be deposited onto platen 30 as a series of roads forprinting 3D part 22 or support structure 24 in a layer-by-layer manner.After the print operation is complete, the resulting 3D part 22 andsupport structure 24 may be removed from chamber 28, and supportstructure 24 may be removed from 3D part 22. 3D part 22 may then undergoone or more additional post-processing steps, as desired.

FIG. 2 is a plan view of an example print head 18, which includes ahousing 44, a drive mechanism 46, and an extruder 20, which are shown inuse with a filament 48. Drive mechanism 46 is a filament drive mechanismthat is configured to feed successive segments of filament 48 from guidetube 16 to extruder 20. In particular, drive mechanism 46 is driven by amotor 60 (e.g., a step motor), based on commands from controllerassembly 38, to feed filament 48 into inlet end 56 a of a liquefier 50in a direction 54.

Liquefier 50 includes a hollow tube 51, which is surrounded by a heaterassembly 62. Hollow tube 51 is generally thin-walled and thermallyconductive and has a geometry that matches the cross-sectional shape offilament 48. Heater assembly 62 is in contact with one or more portionsof hollow tube 51 and includes one or more heating elements thatgenerate and transfer heat to hollow tube 51. The transferred heat meltsthe received filament 48 within hollow tube 51, thereby producing amolten material of filament 48.

Hollow tube 51 is connected to a casing assembly 71, which connects theinterior of hollow tube 51 to the interior of an extrusion nozzle orextruder tip 92. (Casing assembly 71 is not shown to scale in FIG. 2) Insome embodiments, casing assembly 71 also contains a gear pump that isdriven by a motor 84 based on commands from controller assembly 38.Molten material in the interior of hollow tube 51 passes through casingassembly 71 and into the interior of extrusion nozzle 92. Pressurewithin casing assembly 71 forces the molten material out of an orificein nozzle 92 to form an extrudate as discussed further below.

During a printing operation, controller assembly 38 (shown in FIG. 1)commands drive mechanism 46 (via motor 60) (shown in FIG. 2) to feedsuccessive segments of filament 48 into inlet end 56 a of liquefier 50.As filament 48 passes through liquefier 50, heater assembly 62 thermallymelts the received successive segments, where the molten portion of thefilament material forms a meniscus around the unmelted portion offilament 48. The downward movement of filament 48 functions as aviscosity pump to pressurize the molten material and force it fromliquefier 50 into casing assembly 71. The pressurized molten materialthen either exits nozzle 92 based on the pressure provided by thedownward movement of filament 48 or is pumped out of nozzle 92 by a gearpump in casing assembly 71 as discussed in connection with FIG. 3.

FIG. 3 provides a sectional view of casing assembly 71 for an embodimentin which a gear pump assembly 52 is housed within casing assembly 71. Asshown in FIG. 3, gear pump assembly 52 includes heating elements 72 thatextend through and heat casing assembly 71. This prevents the receivedmolten filament materials from cooling down and/or solidifying withingear pump assembly 52 while print head 18 is printing.

Gear pump assembly 52 also includes gears 100 and 104 which are turnedby motor 84. Pressurized molten material flows from hollow tube 51 intoinlet opening 90 of casing assembly 71, as depicted by arrow 116. Thisfills an upper region 118 and inlet opening 90 with the pressurizedmolten material. Engaged teeth 102 and 106 of gears 100 and 104 preventthe received molten material from flowing directly down between gears100 and 104 into outlet opening 94, unless or until the gears arerotated.

Controller assembly 38 may direct motor 84 to rotate gears 100 and 104in directions 120 and 122, respectively. The molten material is thencarried around gears 100 and 104 in the interstitial spaces betweenteeth 102 and 106 and the walls of interior cavity 96 (referred to asinterstitial spaces 123) to a lower region 124 of interior cavity 96, asdepicted by arrows 126 and 128. The continued driving of the moltenmaterial around gears 100 and 104 in this manner forces the moltenmaterial in lower region 124 downward through outlet opening 94 and anorifice 95 of nozzle 92 to extrude the molten material in a controlledmanner, as depicted by arrow 130.

FIG. 4 provides sectional view of an alternative embodiment of casingassembly 71 in which hollow tube 51 and heater assembly 62 extend intocasing assembly 71. The interior of nozzle 92 is connected to theinterior of hollow tube 51 within casing assembly 71, thereby allowingmolten material in hollow tube 51 to flow out of orifice 95 of nozzle 92based on the pressure generated by the downward movement of filament 48.

FIG. 5 provides a top view of neighboring roads under the prior art andFIG. 6 provides a sectional view of FIG. 5 along lines 6-6 of FIG. 5. InFIG. 5, two neighboring roads 500 and 502 have been deposited. As shownin FIG. 6, roads 500 and 502 have obround shapes that include a flat topsurface, such as top surfaces 505 and 504, a flat bottom surface, suchas bottom surfaces 507 and 506 and two rounded side surfaces, such asopposing side surfaces 511 and 512 of road 500 and opposing sidesurfaces 508 and 510 of road 502. As shown in the magnified portion ofFIG. 6, the rounded side ends 512 and 508 of roads 500 and 502 makecontact at a central point 514. However, above and below this point aretwo voids 516 and 518, respectively, where void 518 extends below sidesurfaces 512 and 508 and void 516 extends above side surfaces 512 and508.

Voids 516 and 518 create a weakness in the layer of material since thematerial layer is thinner along the line of contact between roads 500and 502 than at the center of roads 500 and 502. As a result, the linesof contacts between roads tend to be the sites of structural failures inadditive manufacturing parts. To combat this weakness, attempts havebeen made to expand the width of the flat portions of the roads, such aswidth 520 of road 500. However increasing the width of the roads doesnot remove the lines of failure since the roads continue to have roundedsides. In other techniques, when printing a road next to an existingroad, the prior art has attempted to ensure that the orifice of thenozzle extruding the molten material is as close as possible to thepreviously deposited road with the hopes that positioning the nozzle inthis way will force material into the void beneath the previouslydeposited road. Such techniques, however, have been unable to completelyfill the voids because the path of least resistance for the moltenmaterial is away from the previously deposited road. As a result,instead of being forced into the void, the molten material flows awayfrom the previously deposited road without filling the voids.

In accordance with the various embodiments described below, controllerassembly 38 receives tool paths for printing roads such that the roadsare spaced apart from each other. Controller assembly 38 also receivesvoid filling tool paths for filling the voids between the side surfacesof the printed roads. Controller assembly 38 cause the roads to beprinted by sending instructions to move the nozzle along the tool pathsfor the roads while also sending instructions to extrude moltenmaterial. Once the roads are formed, controller assembly 38 sendsinstructions to move the nozzle along the void-filling tool path betweenthe two roads such that a bottom surface of the nozzle remains incontact with the two roads while controller assembly 38 sends controlsignals to extrude material to fill the voids between the two roads.

FIG. 7 provides a top view of two spaced roads 800 and 802 printed inaccordance with one embodiment and FIG. 8 provides a sectional viewalong lines 8-8 of FIG. 7. Road 800 includes flat top and bottomsurfaces 806 and 808 and rounded side surfaces 810 and 812. Similarly,road 802 includes flat top and bottom surfaces 814 and 816 and roundedside surfaces 818 and 820. Controller 38 causes roads 800 and 802 to beprinted based on two tool paths that controller 38 receives. Thepositions of the two tool paths are set such that roads 800 and 802 areseparated by a space or void 804. Space or void 804 has a bead area 824(FIG. 8) that extends above and below rounded side surfaces 812 and 818and is level with top surfaces 806 and 814 and bottom surfaces 808 and816. At the closest point between roads 800 and 802, the roads areseparated by a distance 826. Distance 826 is selected so that it islarge enough to permit molten material to flow between rounded surface812 and rounded surface 818. In addition, distance 826 is selected toensure that portions of nozzle 92 can remain in contact with topsurfaces 806 and 814 while molten material is introduced into space 804.In some embodiments, distance 826 is selected so that it is smaller thanorifice 95 of nozzle 92.

FIGS. 9 shows a top view of a nozzle 92 moving along a void filling toolpath while filling void or space 804. FIG. 10 shows a sectional viewtaken along lines 10-10 of FIG. 9. As shown in FIG. 10, the void fillingtool path received by controller 38 is set such that a bottom surface ofnozzle 92 is in contact with both top surface 806 of spaced road 800 andtop surface 814 of spaced road 802. In FIG. 9, the outer circumference1014 of bottom surface 1002 is shown in phantom. Orifice 95 of nozzle92, has an outer circumference 1016, and is positioned over space 804.In FIG. 9, controller 38 is sending control signals to move nozzle 92 ina direction 1020 along the void filling tool path while also sendingcontrol signals to cause molten material (also referred to as liquefiedmaterial) 1022 to be extruded by orifice 95 thereby forming fill road1000. Because bottom surface 1002 is sealed against top surfaces 806 and814 of spaced roads 800 and 802, the pressure of molten material 1022causes molten material 1022 to be injected into void 804 so that themolten material fills all of bead area 824 of void 804. For example,molten material is injected into void areas 1004 and 1006 below roundedside surfaces 812 and 818 and into void areas 1008 and 1010 aboverounded side surfaces 812 and 818 of spaced roads 800 and 802. Inaddition, molten material fills central void 1012 between the outermostportions of rounded side surfaces 812 and 818. As nozzle 92 moves alongthe void-filling tool space associated with space 804, molten material1022 fills each of the void areas along the path thereby filling volumesabove and below rounded side surfaces 812 and 818.

Portion 1024 of nozzle bottom surface 1002 smooths the top of the moltenmaterial to form a flat top surface 1026 on fill road 1000 that is levelwith top surfaces 806 and 814 of spaced roads 800 and 802. Thus, spacedroads 800 and 802 and fill road 1000 together provide a smoother topsurface than prior art roads, such as those shown in FIGS. 5 and 6 wherethe rounded sides of the roads create a top void 516 that makes the topsurface of the part rough.

The amount of molten material 1022 extruded through orifice 95 whenprinting fill road 1000 is calculated based on the size of bead area824. As shown in FIGS. 11 and 12, for roads of the same height andprofile, the bead area between two roads includes a fixed component anda variable component that varies with the distance between the spacedroads. In particular, in FIGS. 11 and 12, two spaced roads 1100 and 1102are shown with two different separating distances 1104 and 1106respectively. Bead area 1108 for separation distance 1104 includes afixed component constructed from void areas 1110, 1112, 1114 and 1116and a central bead area 1118. Bead area 1120 of FIG. 12 consists of thesame fixed component as bead area 1108, namely void areas 1110, 1112,1114 and 1116. But bead area 1120 has a larger central bead area 1122than central bead area 1118. Comparing central bead areas 1118 and 1122,it can be seen that the difference in the size of these areas is simplya function of the distance between the spaced roads since the heights ofthe central bead areas are the same in both cases. As a result, for agiven height 1140 of the spaced roads, the area for the fixed componentsof the bead area can be calculated once and used for all spaced roadsregardless of the distance between the spaced roads while the size ofthe variable components 1118/1122 are computed as the product of height1140 and the spaced distance 1104/1106 between the spaced roads.

Given the bead area between spaced roads, one or both of the volumetricflow rate of the molten material out of orifice 95 or the velocity ofnozzle 92 can be altered to provide a volume of molten material thatwill fill the bead area as nozzle 92 moves.

FIG. 13 provides a top view of a prior art perimeter and fill patternand FIG. 14 provides a section view along lines 14-14 of FIG. 13. InFIGS. 13 and 14, two perimeter roads 1302 and 1304 have been printed andtwo fill roads 1306 and 1308 have then been printed to fill the spacebetween perimeter roads 1302 and 1304. Space 1310 between fill roads1306 and 1308 is too small to receive a printed road and as a result,space 1310 is left open under the prior art. In addition, since printedroads 1302, 1304, 1306 and 1308 each have rounded side edges, voids,such as voids 1320 and 1322 between roads 1302 and 1306 and voids 1324and 1326 between roads 1304 and 1308 are present in the printed object.These voids along with space 1310 create points of weakness in theprinted part.

FIG. 15 provides a top view of two perimeter roads 1502 and 1504 and twofill roads 1506 and 1508 in accordance with one embodiment. FIG. 16provides a section view along lines 16-16 of FIG. 15. In FIGS. 15 and16, perimeter roads 1502 and 1504 are identical to perimeter roads 1302and 1304 of FIG. 13. Fill roads 1506 and 1508, however, are positioneddifferently than fill roads 1306 and 1308. In particular, controllerassembly 38 has printed road 1506 to create a space 1510 between road1506 and perimeter road 1502. Similarly, road 1508 has been printed tocreate a space 1512 between fill road 1508 and perimeter road 1504.While roads 1506 and 1508 have been printed along tool paths that createspaces 1510 and 1512, they remain separated from each other by a space1514. Each of spaces 1510, 1512 and 1514 have a respective bead area1516, 1518 and 1520. Each bead area extends below and above the roundedside surfaces of the neighboring spaced roads and includes a top surfaceand a bottom surface that are level with the top surfaces and bottomsurfaces, respectively, of the neighboring spaced roads.

FIG. 17 shows the sectional view of FIG. 16 after bead areas 1516 and1518 have been filled with fill roads 1700 and 1702, respectively, andwhile nozzle 92 is filling bead area 1520 with a fill road 1708. Fillroads 1700 and 1702 fill the entirety of bead areas 1516 and 1518,respectively and include top surfaces 1704 and 1706 that are flat and inthe same plane as the top surfaces of spaced roads 1502, 1506 and 1508.While filling bead area 1520, controller assembly 38 moves nozzle 92along a void filling path so that bottom surface 1002 of nozzle 92 is incontact with top surface 1540 of road 1508 and with top surface 1542 ofroad 1504. As a result, molten material 1022 is extruded through orifice95 and is injected into the entirety of bead area 1520 including theportions of the bead area that are beneath and above the curved surfacesof roads 1508 and 1504. The combination of the spaced roads and the fillroads forms a stronger and smother final layer in the embodiment of FIG.17 than the fill patterns of the prior art.

FIG. 18 provides a perspective view of three fill roads 1800, 1802 and1804 relative to a perimeter road 1806 that includes an angled portion1808 under the prior art. As shown in FIG. 18, under the prior art, atthe junction between fill roads 1804 and 1802 and angled portion 1808,two triangular voids 1810 and 1812 are formed. In addition, voids 1814,1816, 1818, 1820, 1822, and 1824 are formed between the neighboringroads of the prior art. These voids create weakness in the parts of theprior art and create roughness on the top surface of parts of the priorart.

FIG. 19 provides a perspective view of a fill pattern relative to aperimeter with an angled portion in accordance with some embodiments. InFIG. 19, controller assembly 38 has printed fill roads 1900, 1902 and1904 and a perimeter road 1906 that has an angled portion 1908.Perimeter road 1906 is identical to perimeter road 1806 of FIG. 18.Roads 1900, 1902 and 1904 are similar to roads 1800, 1802 and 1804 ofthe prior art but are spaced apart from each other by respectivedistances 1910, 1912 and 1914. As a result, controller assembly 38create voids 1920, 1922 and 1924 between roads 1900, 1902, 1904 and 1906as well as triangular voids 1926 and 1928 between roads 1900, 1902, 1904and angled portion 1908 of road 1906. In addition, there is a void 1930between a straight portion 1932 of road 1906 and road 1900. Thedistances 1910, 1912 and 1914 between the spaced roads are selected toallow molten material to flow between the roads while ensuring thatduring the process of depositing the fill roads a portion of the bottomsurface 1002 of nozzle 92 remains in contact with previously depositedspaced roads and/or previously deposited fill roads.

After controller assembly 389 prints the spaced roads of FIG. 19,controller assembly 38 fills the voids between the spaced roads bymoving nozzle 92 along a collection of void filling paths as shown inthe perspective view of FIG. 20. In FIG. 20, void filling road 2000 hasbeen deposited between spaced roads 1900 and 1902 by moving the centerof nozzle 92 along a void filling path 2002 such that a bottom surfaceof nozzle 92 remains in contact with the top surfaces of roads 1900 and1902 while molten material is extruded from orifice 95 of nozzle 92.Because nozzle 92 is sealed against roads 1900 and 1902 when voidfilling road 2000 is extruded, the fill material is injected to fill theentirety of bead area 2004 between roads 1900 and 1902. Similarly, voidfilling road 2006 has been deposited by moving the center of nozzle 92along void filling path 2008 to completely fill bead area 2010 betweenroads 1902 and 1904.

Between roads 1904 and 1906, nozzle 92 has been moved along a voidfilling path 2012 that includes a straight portion 2014 and an angledportion 2016 to form a void filling road 2018. Void filling road 2018completely fills bead area 2017 between roads 1904 and 1906. Bead area2017 has a constant value along straight portion 2014 of tool path 2012and has a decreasing value along angled portion 2016 as the distancebetween road 1906 and road 1904 decreases due to angled portion 1908moving toward road 1904. Thus, along straight tool path portion 2014,the volume of molten material extruded by nozzle 92 remains constantwhile along angled portion 2016, the volume of molten material extrudedby nozzle 92 decreases as nozzle 92 moves along angled portion 2016. Todetermine the volume of molten material that needs to be extruded, thesize of a plurality of different bead areas is determined at a pluralityof different positions along the void filling path between the tworoads.

An additional void filling road 2020 has been deposited between angledportion 1908 and spaced roads 1904 and 1902 and fill roads 2018 and2006. In particular, nozzle 92 has been moved along void filling path2022, which includes portions 2024 and 2026. In moving along voidfilling path 2022, bottom surface 1002 of nozzle 92 is initially incontact with angled portion 1908 of road 1906, a portion of void fillingroad 2108 and with road 1904. Eventually, bottom surface 1002transitions into contact with just angled portion 1908 and spaced road1904 and then into contact with angled portion 1908 and void fillingroad 2006. Bottom surface 1002 then comes in contact with angled portion1908 and road 1902. Along the entirety of void filling path 2022, bottomsurface 1002 of nozzle 92 is in contact with at least two previouslydeposited roads, either spaced roads or previously deposited voidfilling roads. Also, along void filling path 2022, controller assembly38 determines the size of a plurality of different bead areas at aplurality of respective positions.

In FIG. 20, nozzle 92 is currently filling void 1928 and is in contactwith the top surfaces of angled portion 1908 of road 1906, road 1902,void filling road 2000, and road 1900. As a result, molten materialextruded by nozzle 92 is injected into void 1928 such that it fillsportions of the void under the curved side surface of road 1906 andcurved side surface of road 1900. When filling void 1928 and void 1930,nozzle 92 moves along tool path 2030. As it moves along tool path 2030,the bead area being filled varies. As a result, the molten materialand/or the velocity of nozzle 92 is adjusted so that the volume ofmolten material extruded from nozzle 92 fills the entire bead area asnozzle 92 moves along tool path 2030 without providing an excess amountof molten material.

FIG. 21 provides a perspective view of portions of a raster fill road2100 and a boundary or perimeter road 2102 under the prior art. Rasterfill road 2100 includes four road segments 2104, 2106, 2108 and 2110where segments 2104 and 2106 are connected by a raster turnaround 2112and road segments 2108 and 2110 are connected by a raster turnaround2114 and road segments 2108 and 2106 are connected by a rasterturnaround (not shown).

As shown in FIG. 21, raster road segments 2104, 2106, 2108 and 2110 haveflat top and bottom surfaces and rounded side surfaces. The rounded sidesurfaces create voids between the road segments such as top voids 2116,2118 and 2120 and bottom voids 2122, 2124 and 2126. Raster turnarounds2112 and 2114 also have rounded side surfaces and in combination withthe rounded side surfaces of boundary road 2102 create top and bottomvoids, such as top voids 2128 and 2130. In addition, because turnarounds2112 and 2114 are rounded instead of squared, triangular voids areformed between neighboring raster turnarounds and boundary road 2102.For example, triangular voids 2132, 2134 and 2136 are formed byneighboring turnarounds and boundary road 2102. The various voids in theprior art raster fill create weakness in the part and cause the topsurface of the part to have a rough finish.

FIG. 22 provides a perspective view of a raster fill road 2200 and aboundary or perimeter road 2202 in accordance with one embodiment.Raster fill road 2200 includes raster fill segments 2204, 2206, 2208 and2210 with raster segments 2204 and 2206 connected by a raster turnaround2212, raster segments 2208 and 2210 connected by a raster turnaround2214, and raster segments 2206 and 2208 connected by a raster turnaround(not shown). Raster segments 2204 and 2206 are separated from each otherby a distance 2216, raster segments 2208 and 2210 are separated fromeach other by a distance 2218 and raster segments 2206 and 2208 areseparated from each by a distance 2220. In addition, raster turnarounds2212 and 2214 are spaced from boundary road 2202.

In FIG. 22, two void filling roads 2230 and 2232 have been printed withvoid filling road 2230 between road segments 2208 and 2210 and voidfilling road 2232 between road segments 2206 and 2208. Both void fillingroads 2230 and 2232 fill the entire bead area between their respectiveraster road segments. In addition, both void filling roads 2230 and 2232have top surfaces that are aligned with the top surfaces of raster roads2206, 2208 and 2210. Controller assembly 38 forms void filling roads2230 and 2232 by moving nozzle 92 along a void filling path such thatbottom surface 1002 of nozzle 92 is in contact with two neighboringraster road segments to seal the bottom surface of nozzle 92 to theraster roads. As a result, the pressure in molten material 1022 causesthe molten material to be injected beneath and above the rounded sidesurfaces of the raster road segments.

In FIG. 22, nozzle 92 is filling the void between raster road segments2204 and 2206 and bottom surface 1002 of nozzle 92 is in contact withand sealed by the top surfaces of raster road segments 2204 and 2206while molten material is injected into the bead area between the tworoad segments to produce void filling road 2234. Void filling road 2234fills the entire bead area between road segments 2206 and 2204 includingthe voids above and below the curved side surfaces of road segments 2206and 2204. In addition, void filling road 2234 has a top surface that isaligned with the flat surfaces of road segments 2204 and 2206.

FIG. 23 shows a top view of FIG. 22 with an additional two rastersegments 2304 and 2306 that are connected by a raster turnaround 2308,where raster segment 2306 is connected to a raster segment 2204 by araster turn around (not shown). FIG. 23 also includes additional voidfilling roads 2310 and 2312 with void filling road 2310 being betweenraster road segments 2306 and 2204 and void filling road 2312 beingbetween raster road segments 2304 and 2306. In FIG. 23, nozzle 92 isfilling the void between the raster turnarounds 2214, 2212 and 2308 andperimeter or boundary road 2202 by following void filling path 2320. Inparticular, nozzle 92 is filling voids 2132 and 2332, which are eachformed by two neighboring raster turnarounds and boundary road 2202. Inaddition, tool path 2320 fills the space between the turnarounds andboundary road 2202, such as voids 2334 and 2336. By filling the voids,nozzle 92 is constructing void filling road 2340. Along void fillingpath 2320, the bottom surface 1002 of nozzle 92 is in contact with thetop surface of at least two roads such that the pressure of the moltenmaterial causes the molten material to be injected beneath the roundedsurfaces of the raster turnarounds and boundary road 2202. Further, thebottom surface 1002 of nozzle 92 smooths the top surface of fill road2340 so that it is level with the top surfaces of boundary road 2202 andraster turnarounds 2214, 2212, and 2308.

As shown in FIG. 23, the spacing between boundary road 2202 and theraster turnarounds is different from the spacing between boundary road2202 and void filling roads 2232 and 2310. As a result, controllerassembly 38 determines different bead area sizes at different positionsalong void filling path 2320 and the volume of molten material depositedin the voids varies as nozzle 92 moves along void filling path 2320 indirection 2350. For example, more molten material is deposited whennozzle 92 is over void 2132 than when nozzle 92 is over void 2334. Theamount of extruded material can be varied by changing the volumetricflow rate of molten material out of orifice 95 and/or by varying thevelocity of nozzle 92.

As discussed above, the amount of molten material extruded at each pointalong a void filling path can be set based on the bead area at thatpoint. This bead area can be calculated based on the positon andgeometry of the previously deposited roads which are being used to sealthe bottom surface of the nozzle. In some embodiments, the bead areachanges along the void filling path and a different bead area isdetermined at different positions along the void filling path. In otherembodiments, the bead area is not calculated but instead the volumetricflow rate of molten material and/or the velocity of the head are alteredto maintain a desired pressure in the molten material within the nozzle.When the pressure in the nozzle is below a desired pressure, thevolumetric flow rate of the molten material (the amount of extrudedmaterial) is increased and/or the speed of the nozzle is decreased so asto increase the pressure of the molten material and thereby inject themolten material into the entire bead area of the voids. Similarly, ifthe pressure exceeds a threshold such that the molten material isclimbing the exterior of nozzle 92 or spreading along the top surface ofthe previously printed roads, the volumetric flow rate of the moltenmaterial (the amount of extruded material) is decreased and/or thevelocity of nozzle 92 is increased so that the pressure of the moltenmaterial in nozzle 92 decreases.

FIG. 24 provides a sectional view of a nozzle 2400 that maintains apressure of molten material 2402 in nozzle 2400 within a desiredpressure range. In particular, nozzle 2400 includes a strain gauge 2403mounted on the side of nozzle 2400 that is used to indirectly measurethe pressure of molten material 2402. A bottom surface 2408 of nozzle2400 is positioned on roads 2450 and 2452 and nozzle 2400 is extrudingmolten material 2402 into void 2406. As void 2406 fills, molten materialin void 2406 provides a back pressure to molten material 2402 in nozzle2400 and to bottom surface 2408. Since the top of nozzle 2400 issecurely fixed to housing 2410, the increased pressure on bottom surface2408 creates a strain on nozzle 2400 which is measured by strain gauge2403. Strain gauge 2403 provides a sensor signal or strain signal alongconductors 2412 that indicates the strain on nozzle 2400. Controllerassembly 38 uses the sensor signals on conductors 2412 to adjust one ormore of the volumetric flow rate of molten material 2402 and thevelocity of nozzle 2400 to maintain the sensed strain in a desiredrange. This desired range is set so that the pressure of the moltenmaterial 2402 is sufficient to drive or inject the molten materialaround the rounded surfaces of the previously deposited roads 2450 and2452 while being low enough that molten material 2402 does not escapebetween bottom surface 2408 of nozzle 2400 and the top surfaces of roads2450 and 2452.

FIG. 25 provides a sectional view of a nozzle 2500, which is used tomaintain molten material 2502 in nozzle 2500 within a desired pressurerange, in accordance with a further embodiment. Nozzle 2500 includes asidewall through-hole 2504 and a pressure sensor 2506. Molten material2502 passes through hole 2504 so that the pressure of molten material2502 can be sensed by pressure sensor 2506. Pressure sensor 2506provides a sensor value along conductors 2508 to controller assembly138. Based on the sensor values, controller assembly 38 alters thevolumetric flow rate of molten material 2502 and/or the velocity ofnozzle 2500 to maintain the pressure of molten material 2502 within adesired pressure range. This pressure range will ensure that the moltenmaterial is injected into the entire bead area of the void or space 2510between two previously deposited roads 2512 and 2514 while alsopreventing excess molten material from spilling out between the bottomsurface 2516 of nozzle 2500 and the top surfaces of previously depositedroads 2512 and 2514.

FIG. 26 provides an example of a nozzle 2600 that uses an accumulator2602 to maintain the pressure of a molten material 2604 within a desiredrange. Accumulator 2602 is fluidically coupled to the interior of nozzle2600 such that molten material 2604 can move freely between the interiorof accumulator 2602 and the interior of nozzle 2600. In particular,accumulator 2602 includes a piston 2606 that is biased by a spring 2608and moves within a cylinder 2610. When the pressure of molten material2604 exceeds a threshold, the molten material presses against piston2606 and spring 2608 causing the pressure of molten material 2604 todrop. Conversely, when the pressure in the molten material 2604 dropsbelow the threshold, spring 2608 drives piston 2606 to push moltenmaterial out of cylinder 2610 and thereby increase the pressure ofmolten material 2604. Thus, accumulator 2602 provides an open looppressure compensator that is able to maintain the pressure of moltenmaterial 2604 so that the molten material fills the entire bead area2620 between two neighboring roads 2622 and 2624 without causing themolten material to be forced between bottom surface 2626 of nozzle 2600and the top surfaces of roads 2622 and 2624.

FIG. 27 provides a top-down sectional view of a print head 2700 inaccordance with a further embodiment. Print head 2700 includes nozzle 92having orifice 95. Print head 2700 is positioned over two previouslyprinted roads 2702 and 2704 such that a bottom surface of nozzle 92 issealed by the top surfaces of roads 2702 and 2704 and orifice 95 ispositioned over a void 2706 between roads 2702 and 2704. Print head 2700also includes a collection of radar transceivers 2710, 2712, 2714, 2716,2718, 2720, 2722, and 2724. Each radar transceiver is able to transmitan electromagnetic signal toward the part being constructed and toreceive reflected electromagnetic signals from the part. In addition,each radar transceiver generates a radar sensor signal indicative of thestrength of the signal it receives. For example, radar transceiver 2710is able to receive reflected signals from road 2702, 2704 and thesurface below void 2706 and based on the strength of those signalsgenerate a radar sensor signal. The strength of the reflected signal isindicative of the size of the bead area of void 2706 and thus radartransceivers are able to sense the size of the bead area. The sensorsignal is provided to controller assembly 38, which uses the sensorsignal to determine the size of the bead area and to adjust one or moreof the volumetric flow rate or the velocity of nozzle 92 to fill thatbead area when nozzle 92 reaches the position measured by transceiver2710. In the description above, the sensor signal from transceiver 2710was used because print head 2700 is moving in direction 2750 and assuch, radar transceiver 2710 is leading nozzle 92. The collection ofradar sensors is provided so that regardless of the direction of travelof nozzle 92, the bead area of the void being filled can be measured byat least one of the radar transceivers before nozzle 92 reaches thevoid.

FIG. 28 provides a sectional view of a nozzle tip 2800 that can be usedas the end of nozzle 92 with the various embodiments described above.Nozzle tip 2800 includes inner ring or annulus 2890, outer ring orannulus 2892, and an annular recessed groove 2894 locatedcircumferentially between inner ring 2890 and outer ring 2892.

Inner ring 2890 extends circumferentially between tip pipe 2886 andrecessed groove 2894, and has bottom planar face 2888. Inner ring 2890is suitable for printing roads between two previously printed roads soas to inject material below the sides of the two previously printedroads. Outer ring 2892 extends circumferentially around inner ring 2890and recessed groove 2894, and has a knife-edge or substantiallyknife-edge face 2895. Outer ring 2892 seals against the top surfaces ofthe previously deposited roads.

Recessed groove 2894 is an annular groove milled or otherwise formed intip 2800 to separate and define inner ring 2890 and outer ring 2892. Thedimensions of inner ring 2890, outer ring 2892, and recessed groove 2894may vary depending on the desired extrusion profiles. Examples ofsuitable inner diameters for inner ring 2890 (referred to as innerdiameter 2896, corresponding to the diameter of tip pipe 2886) rangefrom about 130 micrometers (about 0.005 inches) to about 640 micrometers(about 0.025 inches), with particularly suitable inner diameters rangingfrom about 250 micrometers (about 0.01 inches)to about 500 micrometers(about 0.02 inches). Examples of suitable outer diameters for inner ring2890 (referred to as outer diameter 2898) range from about 500micrometers (about 0.02 inches) to about 1,300 micrometers (about 0.05inches), with particularly suitable outer diameters ranging from about640 micrometers (about 0.025 inches) to about 900 micrometers (about0.035 inches), where outer diameter 2898 is greater than inner diameter2896. Examples of suitable knife-edge diameters for outer ring 2892(referred to as knife-edge diameter 2899) range from about 1,500micrometers (about 0.06 inches) to about 2,500 micrometers (about 0.10inches), with particularly suitable diameters ranging from about 1,800micrometers (about 0.07 inches) to about 2,300 micrometers (about 0.09inches).

Suitable inner and outer diameters for recessed groove 2894 correspondrespectively to outer diameter 2898 (of inner ring 2890) and knife-edgediameter 2899 (of outer ring 2892). Examples of suitable average depthsfrom bottom face 2888 for recessed groove 2894 (referred to as depth2802) include depths of at least about 250 micrometers (about 0.01inches), and more desirably range from about 500 micrometers (about 0.02inches) to about 1,300 micrometers (about 0.05 inches). As can be seen,recessed groove 2894 is desirably at least a wide as deep.

Although the present disclosure has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the disclosure.

1. A method of additive three-dimensional object production comprising:depositing liquefied material to produce two roads; placing an extrudertip having a bottom surface that surrounds an orifice such that oneportion of the bottom surface is sealed against one of the two roads andanother part of the bottom surface is sealed against the other of thetwo roads and the orifice is positioned over a space between the tworoads; and extruding liquefied material through the orifice to fill thespace between the two roads.
 2. The method of claim 1 wherein each roadhas rounded sides such that extruding liquefied material through theorifice to fill the space between the two roads comprises fillingvolumes above and below the rounded sides of each road.
 3. The method ofclaim 2 wherein extruding liquefied material through the orifice to fillthe space between the two roads comprises determining a bead areabetween the two roads based at least on the position and height of thetwo roads and setting a velocity of the extruder tip and a volumetricflow rate of liquefied material extruded by the extruder tip to provideenough liquefied material to fill the bead area as the extruder tipmoves at the velocity.
 4. The method of claim 3 wherein determining abead area comprises determining a plurality of different bead areasbetween the two roads, each bead area associated with a differentposition of the extruder tip along the two roads.
 5. The method of claim1 wherein depositing liquefied material to produce two roads comprisesdepositing the liquefied material to ensure that the two roads arespaced apart from each other along at least a portion of the two roads.6. The method of claim 1 wherein the space between the roads is smallerthan the orifice.
 7. The method of claim 1 wherein extruding liquefiedmaterial through the orifice to fill the space between the two roadscomprises sensing a pressure of the liquefied material and adjusting avolume flow rate of the liquefied material based on the sensed pressure.8. The method of claim 1 wherein extruding liquefied material throughthe orifice to fill the space between the two roads comprises sensing astrain on the extruder tip and adjusting the volume flow rate of theliquefied material based on the strain.
 9. The method of claim 1 whereinextruding liquefied material through the orifice to fill the spacebetween the two roads comprises providing an accumulator that isfluidically coupled to an interior of the extruder tip such thatliquefied material enters the accumulator when a pressure of theliquefied material in the extruder tip exceeds a threshold pressure andliquefied material exits the accumulator when the pressure of theliquefied material in the extruder tip is below the threshold pressure.10. The method of claim 1 wherein extruding liquefied material throughthe orifice to fill the space between the two roads comprises sensing asize of the space between the roads using a sensor and setting avelocity of the extruder tip and a volumetric flow rate of the liquefiedmaterial to fill the sensed size.
 11. An additive manufacturing systemcomprising: a nozzle having an orifice surround by a bottom surface; anda controller: receiving instructions to print along two tool paths andto print along a void filling path between the two tool paths; sendingcontrol signals to print two roads corresponding to the two tool paths;and sending control signals to move the nozzle along the void fillingpath between the two roads such that the two roads remain in contactwith the bottom surface of the nozzle while the controller also sendscontrol signals to extrude material to fill a void between the tworoads.
 12. The additive manufacturing system of claim 11 wherein thevoid between the two roads extends underneath a portion of at least oneof the two roads.
 13. The additive manufacturing system of claim 11wherein sending control signals to move the nozzle along the voidfilling path and sending control signals to extrude material to fill avoid between the two roads comprises determining a bead area between thetwo roads and setting a velocity for the nozzle and a volumetric flowrate for the extruded material to fill the bead area.
 14. The additivemanufacturing system of claim 11 wherein the bead area varies along thevoid filling path.
 15. The additive manufacturing system of claim 11further comprising a pressure sensor that senses a pressure of materialin the nozzle to produce a pressure signal, wherein the controller usesthe pressure signal to adjust at least one of a velocity of the nozzleand a volumetric flow rate of the extruded material.
 16. The additivemanufacturing system of claim 11 further comprises a strain sensor thatsenses a strain on the nozzle to produce a strain signal, wherein thecontroller uses the strain signal to adjust at least one of a velocityof the nozzle and a volumetric flow rate of the extruded material. 17.The additive manufacturing system of claim 11 further comprises a radarsensor that senses a space between the two roads to produce a radarsensor signal, wherein the controller uses the radar sensor signal toadjust at least one of a velocity of the nozzle and a volumetric flowrate of the extruded material.
 18. The additive manufacturing system ofclaim 11 further comprises an accumulator that is fluidically coupled toan interior of the nozzle such that material moves into the accumulatorwhen a pressure of the material in the nozzle exceeds a thresholdpressure and material moves out of the accumulator when the pressure ofthe material in the nozzle is below the threshold.
 19. A methodcomprises extruding material from an extruder tip of an additivemanufacturing system such that the extruded material flows beneath andbetween portions of two previously extruded roads of material.
 20. Themethod of claim 19 wherein extruding material from the extruder tipcomprises placing the extruder tip in contact with the two previouslyextruded roads while extruding the material.
 21. The method of claim 20further comprising using a pressure of the extruded material to controlan amount of extruded material that is extruded from the extruder tip.22. The method of claim 21 wherein using the pressure of the extrudedmaterial comprises sensing a strain on the extruder tip caused by thepressure of the extruded material and using the sensed strain to controlthe amount of extruded material.
 23. The method of claim 21 whereinusing the pressure of the extruded material comprises sensing thepressure of the material in the extruder tip and using the sensedpressured to control the amount of extruded material.